We don't hear much about it today, but growing enough food to feed the planet will be a significant problem before long unless we make some changes soon.

A leading cause of the projected food squeeze is that agricultural productivity has not increased as fast this decade as it did during the second half of the 20th century. In other words, we are starting to consume more than we're producing..

The global population has grown at roughly 2 percent a year, but that trend understates the increase in demand for food. Standards of living in emerging markets such as China have risen, leading to increased consumption of items further up the food chain, such as meat. And those richer foodstuffs require more calories and energy (fertilizer) to produce than the basic grain diets on which the world's poor have traditionally relied.

Starting with the Green Revolution in the 1960s, there has been a fairly steady increase in food yield per acre of 2 percent or more per year. But there has been no new big round of technology that increases crop yield since then, and new factors are coming into play, such as more severe weather disruption (due in part to global warming); increased land degradation and loss of irrigation water, and shrinking available arable land to expand agriculture.

And as global warming accelerates, the consequences will severely reduce our agricultural production because of droughts, storms, flooding, and temperature increases in key growing zones, such as the American Midwest.

But there's a huge opportunity that would help reverse the trends. "From farm to fork," as the experts say, how much food do you think is wasted, lost, thrown away, spoiled or otherwise not used? The answer: a staggering 30 percent globally.

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In the United States, nearly 40 million tons of food a year ends up in landfills, according to the Food Waste Reduction Alliance, an industry group that has started to wrestle with this problem.

Most demographers predict that the world's population will stabilize somewhere between 9 billion and 10 billion in roughly two decades. One of the very few courses that will allow us to feed this many people is to reduce food waste.

Of course this is a problem for the food industry. If you make money by producing, distributing or selling food, then the more you produce, process or sell, the more you earn. This is true whether you're a farmer or Campbell Soup Co. So if demand goes up, to the degree you can get waste out of your production chain, the more you will sell and the more you will make.

But if one of the places we eliminate waste is that part of the food chain that stretches from the point of sale, such as the supermarket, to your dining room table, that means families will be buying less food -- and that is not a happy prospect if you're in the food business.

If gains in agricultural productivity continue to decelerate, and if the pressure on crops placed by global warming increases -- and both trends seem firmly established -- we will have no other choice than to go after food waste.

The Europeans are ahead of us on this issue. There are organizations and websites in Europe that alert people to the problem of food waste. And some supermarkets in Germany and the United Kingdom sell what's called "ugly food" -- food that has passed its best sell-by date but is still safe to eat.

If you don't want to pay top price for food and you'd like to reduce food waste, then "ugly food" is for you.